Miniaturization of devices in the chemical, pharmaceutical and biotechnological field has lead to the development of microfluidic devices that control the flow of liquid and permit the performance of a number of chemical and biological reactions. However, such devices do not allow downscaling a conventional, general-purpose chemistry laboratory onto a single microchip due to the lack of appropriate microcomponents, such as microseparators or microfilters. Furthermore, such devices do often not meet mixing requirements. Therefore, an open-well design, typically a multiwell-plate, is frequently employed in combination with automated mixing- and washing devices. However, such a well design poses increasing challenges upon further miniaturization and one of its major problems is evaporation.
The manipulation of droplets has recently received considerable interest due to the possibility of isolating and handling volumes down to the picoliter/femtoliter range (cf. e.g. international patent application WO 2004/030820). Several lab-on-a-chip (LOC), micro total analysis (μTAS), and biological microelectromechanical systems (BioMEMS) have been developed for moving, merging/mixing, splitting, and heating of droplets on surfaces, such as electrowetting-on-dielectric (EWOD) [Pollack, M. G. et al., Appl. Phys. Lett. (2000), 77, 1725-1726], surface acoustic waves (SAW) [Wixforth, A. et al., mstnews (2002), 5, 42-43], dielectrophoresis [Cascoyne, P. R. C. et al., Lab-on-a-Chip (2004), 4, 299-309], and locally asymmetric environments [Daniel, S. et al., Langmuir (2005), 21, 4240-4228]. However, these methods lack the most important operation for performing sequential biological processes: the ability to separate/purify/isolate starting material and/or reaction products from crude or complex mixtures. In order to permit such a separation a solid phase needs to be introduced as part of the droplet-based system.
Accordingly, it is an object of the present invention to provide a method for processing a chemical and/or biological sample, which avoids these discussed disadvantages.